The present invention relates to methods and systems for detecting abnormalities, such as cancer and pathological conditions, in cells and tissues using optical, or spectroscopic techniques.
More specifically, the methods and apparatus of the present invention relate to the use of contrast enhancing agents in connection with optical spectroscopic techniques to distinguish abnormal or pathological tissue, such as cancerous tissue, from normal tissue and to grade and characterize cancerous tissue.
Methods and systems for identifying abnormal or pathological cells and tissue, particularly cancer, and for diagnosing cancerous conditions, are generally time consuming and invasive. Furthermore, many of the screening techniques currently available provide limited sensitivity and specificity. Tissue biopsies or samples may be taken, fixed and examined using various histological techniques. Since these diagnostic procedures are both invasive and expensive, and they are very stressful for patients undergoing testing, it is desirable to screen areas of suspected abnormalities first, to eliminate unnecessary trauma and expense. Diagnostic screening techniques used for detecting breast cancer, uterine and cervical cancers, colon and colo-rectal cancers, esophageal cancer and skin cancers are generally inadequate and unreliable. It is thus a high priority to develop methods and systems providing reliable, non-invasive screening techniques for identifying cancer cells that have a high degree of sensitivity and specificity.
The diagnostic value of performing a biopsy is dependent upon the selection of tissue for sampling. Many pathologies are not uniformly distributed and, therefore, the selection of tissue for sampling may be determinative of the diagnostic outcome. Additionally, unnecessary removal of tissue may result in localized trauma and, in some cases, may result in diminished function. Taking tissue samples from lymph nodes, for example, is essential to assess the progression of many cancers. Yet, removal of too much tissue, or removal of normal localized tissue having a specialized function may result in diminished function. It is therefore essential to identify and sample tissue that has the highest likelihood of including pathological cells, while avoiding the removal of healthy tissue.
A primary means for treatment of pathologies, such as cancer, is surgical removal. Many studies have shown that the clinical outcome is improved when more of the total amount of tumor tissue is removed. For gross total resections of tumors, the five year survival rate is significantly increased compared to subtotal resection. Both duration of survival and independent status of the patient are prolonged when the extent of resection is maximized in cancerous tissue. Current intraoperative techniques do not provide rapid differentiation of tumor tissue from normal surrounding tissue, however, particularly after resection of the tumor begins. Development of techniques that enhance the ability to identify tumor tissue intraoperatively may result in maximizing the degree of tumor resection, thereby prolonging survival.
Most current tumor detection techniques are performed prior to surgery to provide information about tumor location. Pre-surgical imaging methods include magnetic resonance imaging (MRI) and computerized tomography (CT). In the operating room, intraoperative ultrasound and stereotaxic systems provide information about the location of tumors. Ultrasound shows the location of the tumor from the surface but, once surgery begins, ultrasound techniques do not provide information sufficient to prevent the destruction of important functional tissue while permitting maximal removal of tumor tissue. Stereotaxic systems coupled with advanced imaging techniques have, at select hospitals, provided localization of tumor margins based upon the preoperative CT or MRI scans. However, studies have shown that the location of the tumor changes, particularly during invasive surgeries, and the actual tumor may extend 2-3 cm beyond where the image enhanced putative tumor is located on preoperative images.
One method currently available for determining the location of tumors is to obtain multiple biopsies during surgery and wait for results of microscopic examination of sections. This technique, known as multiple histological margin sampling, suffers several drawbacks. First, this is a time-consuming procedure and can add about 30 to 90 minutes (depending upon the number of samples taken) to the length of time the patient is under anesthesia. The increased time required for margin sampling leads to increased medical costs, as operating room time costs are high. Moreover, increased operating room time for the patient increases the probability of infection and complications arising from the anesthesia. Multiple histological margin sampling is prone to errors, as the pathologist must prepare and evaluate samples in short order. In addition, margin sampling does not truly evaluate all regions surrounding a primary tumor and some areas of residual tumor can be missed due to sampling error.
Thus, although patient outcome is dependent upon aggressive removal of tumor tissue, a surgeon often does not have reliable intraoperative information concerning the location and extent of the tumor. Surgeons must make difficult decisions between aggressively removing tissue and destroying surrounding functional tissue, and they may not know the true outcome of the procedure until permanent tissue sections are available about one week later. Additional surgical procedures may be required following examination of the histological studies.
Other techniques developed to improve imaging of solid tumor masses during surgery include determining the shape of visible luminescence spectra from normal and cancerous tissue. U.S. Pat. No. 4,930,516 teaches that the shape of visible luminescence spectra from normal and cancerous tissue are different. Specifically, there is a shift to blue with different luminescent intensity peaks in cancerous tissue as compared to normal tissue. Thus it is possible to distinguish cancerous tissue by exciting the tissue with a beam of ultraviolet (UV) light and comparing visible native luminescence emitted from the tissue with luminescence from a non-cancerous control of the same tissue type. Such a procedure is fraught with difficulties since a real time, spatial map of the tumor location is not provided for the use of a surgeon. Moreover, the use of UV light at an excitation wavelength can cause photodynamic changes to normal cells and is dangerous for use in an operating room. In addition, UV light penetrates only superficially into tissue and requires quartz optical components instead of glass.
Following the identification and localization of malignant tissue, or following surgical removal of malignant tissue, it is important to monitor the tissue in the area of malignancy for the reappearance or spreading of malignant tissue. Similarly, monitoring an area of interest such as malignant tissue during and/or following treatment with drugs, radiation therapy, or the like, is necessary to assess the efficacy of the treatment and to monitor the progression or recession of the malignancy. Convenient, inexpensive and minimally invasive techniques are desirable for performing these monitoring functions, and few effective systems are available.
U.S. Pat. No. 5,438,989 discloses a method for imaging margins, grade and dimensions of solid tumor tissue by illuminating the area of interest with high intensity electromagnetic radiation containing a wavelength absorbed by a contrast agent, obtaining a background video image of the area of interest, administering a contrast agent, and obtaining subsequent video images that, when compared with the background image, identify the solid tumor tissue as an area of changed absorption. U.S. Pat. No. 5,699,798 discloses methods and apparatus for optically distinguishing between tumor and non-tumor tissue, and imaging margins and dimensions of tumors during surgical or diagnostic procedures.
U.S. Pat. No. 5,465,718 discloses a method for imaging tumor tissue adjacent to nerve tissue to aid in selective resection of tumor tissue using stimulation of a nerve with an appropriate paradigm to activate the nerve, permitting imaging of the active nerve. The ""718 patent also discloses methods for imaging of cortical functional areas and dysfunctional areas, methods for visualizing intrinsic signals, and methods for enhancing the sensitivity and contrast of images. U.S. Pat. No. 5,845,639 discloses optical imaging methods and apparatus for detecting differences in blood flow rates and flow changes, as well as cortical areas of neuronal inhibition.
The methods and systems described herein distinguish between normal and abnormal, or pathological tissue, such as cancerous tissue, using optical (spectroscopic) detection techniques and contrast enhancing agents, and aid in identifying pathological tissue during surgical, diagnostic, monitoring and biopsy procedures. For example, optical detection techniques of the present invention may be used in diagnostic screening applications to identify pathological tissue, such as cancerous tissue. In addition, the methods and apparatus of the present invention are used to identify margins and dimensions of pathological tissue during surgical procedures, and to grade and characterize pathological tissue, particularly cancerous tissue. Additionally, methods and systems of the present invention may be used as a biopsy aid to identify potentially abnormal tissue that should be included in a biopsy sample; for monitoring the progression or recession of a pathological condition, such as cancer; and/or for monitoring the efficacy of treatment agents or protocols. The optical detection techniques of the present invention provide information and results in xe2x80x9creal-timexe2x80x9d and with a high degree of spatial resolution, and thus may be used intraoperatively or be interfaced with stereotaxic systems used during surgical procedures to accurately locate the malignant tissue during surgeries.
The use of contrast-enhancing agents provides data having high sensitivity and specificity, and thus enhanced reliability, and is therefore preferred in conjunction with implementation of the methods and systems described herein. Contrast enhancing agents provide differential optical contrast between normal, functional, and pathological tissue, providing differential contrast enhancement between normal and abnormal tissue. Thus, using the methods and systems described herein, it is possible to identify and differentiate abnormal or pathological tissue from surrounding normal tissue by detecting changes in the optical properties of a tissue sample in situ.
Contrast enhancing agents suitable for use in the present invention enhance differences in the optical properties, or optical contrast, between normal and abnormal tissue. Administration of contrast enhancing agents may, for example, change optical absorption properties, optical scattering properties, birefringence, or the like, differentially in normal and abnormal cells. Alternatively or additionally, contrast enhancing agents may exhibit different dynamics, such as different perfusion rates, clearance rates, or the like, in normal and abnormal tissue or may sequester preferentially in abnormal tissue. For some applications, it may be desirable to employ multiple contrast enhancing agents, each agent having different spectral properties. The contrast enhancing agents are non-toxic to normal cells and do not interfere with normal metabolic activities at the area of interest.
Examples of contrast enhancing agents include fluorescent and phosphorescent materials, photodynamic dyes, indocyanines, fluoresceins, hematoporphyrins, and fluoresdamines, agents that are used topically, such as iodine, weak acidic and basic agents, and the like. The contrast enhancing agent may be administered intravenously, intraarterially, subcutaneously, topically, or using any route of administration that delivers the agent to the area of interest. Indocyanine green, which has a broad absorption wavelength range and a peak absorption in the range of 730 nm to 840 nm, is a suitable contrast enhancing agent for detection of cancerous tissue in diagnostic and intraoperative procedures. Iodine and weak acidic and basic agents are suitable contrast enhancing agents for topical application and screening for cancerous tissue on the surface of tissue, such as cervical tissue, colo-rectal tissue, intestinal system tissue, and the like. Agents that preferentially sequester in abnormal or pathological tissue may be used. Detectors appropriate for use with the contrast enhancing agents employed with methods and systems of the present invention are well known in the art.
The systems of the present invention employ one or more electromagnetic radiation (emr) optical source(s) for illuminating an area of interest (i.e., an area to be screened or an area believed to contain abnormal or pathological tissue), and one or more optical detector(s) capable of detecting and acquiring data relating to one or more optical properties of the area of interest. The optical source(s) and detector(s) may be selected and located to acquire data relating to optical properties of an area of interest that is exposed, or that underlies skin, tissue, bone, dura, or the like. Epi-illumination and reflective detection are preferred for many applications. For some applications, transillumination techniques are used, following administration of a contrast enhancing agent, to identify abnormalities within a tissue sample in situ, such as a breast.
The optical detector(s) may be used to acquire data for analysis in a static mode, or multiple data sets may be acquired at various time intervals for comparison in a dynamic mode. The optical detector(s) may, for example, acquire control data representing the xe2x80x9cnormalxe2x80x9d or xe2x80x9cbackgroundxe2x80x9d optical properties of an area of interest, and then acquire subsequent data representing the optical properties of an area of interest following administration of a contrast-enhancing agent, or during a monitoring interval. The subsequent data is compared to the control data, or to empirically determined standards, to identify changes in optical properties of corresponding spatial locations in the data set that are representative of normal and abnormal tissue.
Optical source(s) may provide continuous or non-continuous illumination. Various types of optical detectors may be used, depending on the emr source(s) used, the optical property being detected, the type of data being collected, certain properties of the area of interest, the desired data processing operations, the format in which the data is displayed, and the type of application, e.g., intraoperative, diagnostic, biopsy, monitoring, or the like. For some applications, emr sources providing continuous, uniform illumination are preferred, while non-continuous illumination using time domain or frequency domain illumination sources are preferred for some applications.
Changes in optical properties that may be indicative of abnormalities include, for example, reflection, refraction, diffraction, absorption, scattering, birefringence, refractive index, Kerr effect, and the like. The optical source and detection system may be incorporated in an apparatus for use external to the area of interest, or optical detection components may be mounted in an invasive or semi-invasive system, such as an endoscope, laparoscope, biopsy device or probe, or may be provided as individual optical fibers or bundles of optical fibers, or the like.
Numerous devices for acquiring, processing and displaying data representative of one or more optical properties of spatially localized and identified areas in an area of interest can be employed. In general, any type of photon detector may be utilized as an optical detector. The optical detector generally includes photon sensitive elements and optical elements that enhance or process the detected optical signals, such as lenses, polarizers, objectives, and the like. In a simple form, the apparatus of the present invention may include one or more optical fibers operably connected to one or more emr sources that illuminates tissue, with corresponding optical fibers operably connected to an optical detector, such as a photodiode, that detects one or more optical properties of the illuminated tissue. According to another embodiment, a video camera acquires control and subsequent images of an area of interest that can then be compared to identify areas of abnormal tissue. Examination of such data elucidates the precise spatial location of tissue abnormalities and permits characterization of abnormal tissue, such as cancerous tissue. Apparatus and methods suitable for obtaining data relating to one or more optical properties of an area of interest have been described in the patents incorporated herein by reference and are more fully described below.
For most surgical, diagnostic, and monitoring uses, the optical detector preferably provides data having a high degree of spatial resolution at a magnification sufficient to precisely locate the margins of abnormal tissue, such as tumors and cancerous tissue. Several data sets are preferably acquired over a predetermined time period and combined, such as by averaging, to provide data sets for analysis and comparison. Methods and systems of the present invention may be used in a static mode that provides a comparison of optical properties of different spatial locations in an area of interest, to spatially locate areas showing differential contrast enhancement and thereby locate areas of normal and abnormal tissue. A comparison of optical properties of two different areas of interest may also be made in a static mode. Thus, following administration of a contrast enhancing agent, an area of interest believed to contain abnormal tissue may be compared to another area of interest of the same type of tissue believed to contain normal tissue. In this embodiment, the presumed normal area of interest provides the control, or background data set for comparison with the area of interest believed to contain abnormal tissue.
Operation of methods and systems of the present invention in a dynamic mode compares data acquired from corresponding spatial locations at various time points. While it is preferred, for many applications, to acquire control data sets from the area of interest of each patient prior to administration of the contrast enhancing agent to compare with subsequent data sets acquired from the same area of interest in the same patient subsequent to administration of the contrast enhancing agent, it is also possible to compare data sets acquired following administration of a contrast enhancing agent to empirically determined standard or control data sets.
Various data processing techniques may be advantageously used to assess the data collected in accordance with the present invention. Data may be analyzed and displayed in a variety of formats. Processing may include averaging or otherwise combining a plurality of data sets to produce control, subsequent or comparison data sets. Other optical data processing techniques include frequency domain methods such as Fourier or wavelett transformations of the optical data, or spatial domain methods such as convolutions, geometrical transformations, data differencing, and the like.
Data processing may also include amplification of certain signals or portions of a data set (e.g., areas of an image) to enhance the contrast seen in data set comparisons, and to thereby identify areas of abnormal tissue with a high degree of spatial resolution. For example, according to one embodiment, images are processed using a transformation in which data point brightness values are remapped to cover a broader dynamic range of values. A xe2x80x9clowxe2x80x9d value may be selected and mapped to zero, with all data point brightness values at or below the low value set to zero, and a xe2x80x9chighxe2x80x9d value may be selected and mapped to a selected value, with all data point brightness values at or above the high value mapped to the high value. Data having an intermediate brightness value, representing the dynamic changes in brightness indicative of changes in optical properties, may be mapped to linearly or logarithmically increasing brightness values. This type of processing manipulation is frequently referred to as a xe2x80x9chistogram stretchxe2x80x9d or point transformation, and can be used according to the present invention to enhance the contrast of data sets, such as images, representing differences in tissue type.
Data processing techniques may also be used to manipulate data sets to provide more accurate combined and comparison data. For example, patient movement, respiration, heartbeat or reflex activity may shift an area of interest during detection of optical properties and data collection. It is important that corresponding data points in data sets (such as corresponding pixels of an image) are precisely aligned, spatially, to provide accurate combined and comparison data. Such alignment may be accomplished manually by a practitioner having specialized skill and expertise, or using a variety of mechanical and/or mathematical means. Emr source(s) and optical detector(s) may, for example, be mounted in a relatively xe2x80x9cfixedxe2x80x9d condition in proximity to an area of interest. Optical markers may be fixed at an area of interest and detected as the data is collected to aid in manual alignment or mathematical manipulation. Motion artifacts may be reduced or substantially eliminated by timing the acquisition of data to the cycle of respiration, heartbeat, or the like, to normalize the data. Various processing techniques are described below and in the patents incorporated herein by reference.
Comparison data may be displayed in a variety of ways. For example, comparison data may be displayed in a graphical format that highlights optical differences differentiating normal from abnormal tissue. A preferred technique for presenting and displaying comparison data is in the form of visual images, or photographic frames, corresponding to the area of interest. This format provides a visualizable spatial location (two- or three-dimensional) of an area of interest that is useful for treatment, diagnosis and monitoring.
To enhance and provide better visualization of optical contrast between abnormal and normal tissue, comparison images may be processed to provide an enhanced contrast grey scale or even a color image. A look up table (xe2x80x9cLUTxe2x80x9d) may be provided, for example, that converts the gray scale values for each pixel to a different (higher contrast) gray scale value, or to a color value. Color values may map to a range of grey scale values, or color may be used to distinguish between positive-going and negative-going optical changes. In general, color-converted images provide higher contrast images that highlight changes in optical properties representing areas of malignant and normal tissue.
In operation, an area of interest in a patient is illuminated with electromagnetic radiation (emr) while one or a series of data points or data sets representing one or more optical properties of spatially definable areas in the area of interest is acquired. Data sets are acquired before and/or after the administration of a contrast enhancing agent. The area of interest may be exposed to the emr source(s), or may underlie skin, tissue, bone, dura, or the like, provided that the emr source(s) is selected and positioned to penetrate tissue overlying the area of interest. Alternatively, the area of interest may be located within tissue, and the emr source(s) and detector(s) selected and positioned for transillumination of the area of interest.
For operation in a static mode, a contrast enhancing agent is administered, such as by injection or topical application, to an area of interest, and a data set mapping one or more optical properties to spatial locations in the area of interest is acquired. Spatial locations evidencing contrasting optical properties highlight areas of normal and abnormal tissue. Application of a topical contrast enhancing agent such as iodine or a weak acidic or basic agent to the surface of an area of interest, such as cervical tissue, colo-rectal tissue, digestive system tissue, esophageal tissue, or the like, for example, is followed by illumination of the area of interest and detection of differential optical properties at different spatial locations within the area of interest. Similarly, injections of a contrast enhancing agent, such as indocyanine green, followed by illumination of the area of interest and detection of differential optical properties corresponding to different spatial locations within the area of interest, provides differentiation and spatial localization of abnormal tissue, such as cancerous tissue, from surrounding normal tissue.
Additionally, operation in a static mode may involve illumination and acquisition of data sets from two spatially separated locations and comparison of the data sets at one or more time points following administration of the contrast enhancing agent. Thus, for example, data representative of the optical properties of two different areas of breast tissue may be acquired at predetermined time intervals following administration of a contrast enhancing agent, such as indocyanine green. One of the areas of interest is presumed to contain xe2x80x9cnormalxe2x80x9d tissue. Data from the xe2x80x9cnormalxe2x80x9d area of interest is compared to data from another area of interest to detect and spatially localize differential optical properties that are indicative of abnormal tissue.
Acquired data may be compared to control or background data during operation in a static or a dynamic mode. Control data may represent standards derived from optical properties of empirical data samples of desired tissue populations. Control data may thus be derived representing various normal tissue types as well as various abnormal tissue types, such as different types and grades of tumors. Comparison of data acquired following administration of a contrast enhancing agent to various types of control data may then provide identification and spatial localization of abnormal tissue, such as cancer, as well as typing of the abnormal tissue, such as identifying particular cancers, and grading of cancerous tissue. For abnormalities such as cancer, it may be desirable to compare multiple data sets acquired at intervals following administration of the contrast enhancing agent to control data to observe changes in the optical properties of tissue at the area of interest at predetermined time intervals following administration of the contrast enhancing agent. According to one embodiment, statistically significant, contrast enhanced changes in optical properties of tissue may be determined empirically for various types of tissue, cancers, contrast enhancing agents and the like. Comparison of a data set acquired following administration of a contrast enhancing agent to a control data set representing statistically significant changes provides identification of spatial locations within an area of interest evidencing statistically significant changes indicative of abnormalities.
In another dynamic mode, data acquired corresponding to an optical property of an area of interest prior to administration of a contrast enhancing agent represents control, or background, data. A series of data sets is preferably combined, for example by averaging, to obtain a control data set. The control data set is stored for comparison with data collected subsequently. Alternatively, control or background data corresponding to various conditions of tissue and areas of interest may be acquired, stored, and used for comparison. Control data sets may also be acquired, in real time, from an area of interest believed to contain normal tissue. A subsequent data set representing the corresponding optical property is acquired during a subsequent time period following administration of a contrast enhancing agent. A series of subsequent data sets is preferably combined, for example by averaging, to obtain a subsequent data set. Subsequent data sets are compared with one or more control data set(s) to obtain comparison data set(s), preferably difference data set(s). Comparison data sets are then examined for evidence of changes in optical properties representative of areas of abnormal versus normal tissue within an area of interest.
According to one embodiment, the methods and systems described herein may be employed to obtain three-dimensional information of an area of interest suspected to contain abnormal tissue by: (a) illuminating the area of interest with a least two different wavelengths of emr; (b) obtaining a sequence of control data sets corresponding to each wavelength of emr; (c) administering a contrasting enhancing agent; (d) obtaining a sequence of subsequent data sets for each wavelength of emr; (e) obtaining a series of comparison data sets for each wavelength of light by subtracting the control data set from the subsequent data set or alternatively, in the case of fluorescent dyes, subtracting the subsequent image from the control image; and (f) obtaining an enhanced comparison data set by ratioing the first comparison data set to the second comparison data set. Data corresponding to three dimensional spatial locations may also be acquired using multiple contrast enhancing agents having different spectral properties, and by employing optical tomography techniques. Specifically, photon time-of-flight techniques and frequency domain methods may also be used.